Alkaline leaching of lead and zinc by sodium hydroxide: kinetics modeling

This study was performed in two phases of work. In the first stage, alkaline leaching of lead and zinc from an Iranian low-grade oxide ore was examined and the influence of the operating variables including stirring speed, leaching temperature, NaOH concentration and liquid to solid ratio was determined experimentally. The optimum condition was found to be NaOH concentration of 4 M, liquid to solid ratio of 20 ml/g, temperature of 80 °C and a stirring speed of 500 rpm for lead and 400 rpm for zinc, in the range of investigated parameters. Under these conditions, the highest recovery of lead and zinc was obtained to be 72.15 and 85.52%, respectively. In the second stage, the dissolution kinetics of lead and zinc was evaluated by the shrinking core models. The finding reveals that diffusion through the fluid film was the leaching kinetics rate controlling step of lead and zinc. The activation energy was found to be 13.6 kJ/mol for lead and 13.92 kJ/mol for zinc. Equations representing the leaching kinetics of lead and zinc were achieved to be 1 − (1 − x)2/3 = 0.7272 × e(−13.6/(8.314×T)) × t and 1 − (1 − x)2/3 = 0.9686 × e(−13.92/(8.314×T)) × t, respectively.